Alloy steels



Patented June 11, 1935 UNITED STATE ALLOY STEELS Joel Larsson, Hofors, Sweden, and Haakon Styri,

Philadelphia, Pa., assignors, by ments, to S K F Industries, Inc.,

mesne assign- Philadelphia,

Pa., a corporation of Delaware No Drawi g.

Application December 2, 1932,

' Serial No. 645,412 Claims. (Cl. 308-242) This invention relates to steel and has for an ob ect to provide an alloy steel possessing characteristics' imparting to objects'formed from it highly desirable behavior when subjected to 5 quenching during heat treatment, and having a carbon content over the so-called eutect id or pearlite point of steel and having approximately: one per cent or more of manganese, one per cent or more of chromium and one-half per cent or more of silicon; the sum of manganese, chromium and silicon being not less than two and one-half per cent nor more than five per cent, the balance .of the alloy being substantially iron. with the usual commercial impurities.

One advantage in making steel having the foregoing percentages of silicon and manganese is that the alloy substances may be added in the form of ferro silicon manganese, whereby the carbon content can be more carefully controlled and, as results would indicate, a steel free from slag inclusions will be obtained.

The features of advantage possessed by the alloy steel, the subject of the present invention, can best be demonstrated by briefly reviewing the undesirable features which developed in heat treating objects formed from other steels.

A steel which, at the present time, is used by some ball bearing manufacturers has been standardized by the Society of Automotive Engineers as Number 52100. The formula of this steel has the following percentages: carbon .95-l.10, manganese .20-.50, silicon less than .30, chromium 1.20-1.50. This steel is quite satisfactory for small and medium sized bearing parts, but is not satisfactory for larger dimensions because it is not possible to oil quench to satisfactory hardness, and water quenching is dangerous due to the production of cracks.

The anti-friction bearing manufacturing company with which these present inventors are .as-

a higher manganese steel, but with lower carbon content, this being about .90-1.00 manganese and .60-.'70 carbon, .90-1.15 chromium.

This steel showed better hardening properties than standard bearing steel, but was unsatisfactory from a structural point of view as it would easily become coarse in hardening and diflicult to produce the steel with uniformity,

Later we tried a steel with a higher carbon, also with the higher manganese, and found that the hardening properties improved, and also that the endurance of the hardened articles was satisfactory. Thisimprovement encouraged further efforts in the same direction, and we found by trial that it was desirable to have carbon over the so-called eutectoid or pearlite point of steel, which for lower alloy steels is about .85 per cent, together with about 1 per cent manganese and 1 per 'cent chrome. These steels were quite satissociated tried it was also.

factory from a hardening point of view, but there were objections to this steel due to irregularity of production Therefore it was tried to facilitate the production by increasing the silicon contentsimultaneously with The result of these efforts was the manganese content. a clean steel that showed very good hardening properties for sections which were at least 50 per cent greater than the maximum section of the standard steel which would be hardened in oil.

The analysis which we worked out, and sub sequently adopted, was 1 percent carbon, cent manganese, l per cent chromium and .6 per cent silicon.

An alloy steel of this character is easily handled in all manufacturing operations including melting, annealing, machining and hardening.

Further developments indicated to us that it was desirable to increase the alloy content in order to be able to heat treat still heaviersections as. demanded in the more modern practices of the ball and roller bearing industry. We then tried an increase in chromium and man ganese which, as we had expected, facilitated deep hardening. It is of. interest to note in this connection that the volume changes for such steels in hardening are not as great after oil quenching as for the standard bearing steel, and that they can be quenchedfrom slightly lower temperatures provided the chromium by itself. is not too high. It is even possible, in special cases, to heat treatin water large sections made of this material. v

It should be noted that a satisfactory structure is not obtained if the carbon is lowsimiil taneously with low manganese and chromium, andwe therefore believe that persons'op'erating under the disclosure of this patent shouldbear in mind that the carbon should not be less than .85 per cent and chromium not less than .90 per cent. The lower range of alloy content and the higher carbon should then be used for small dimensions of material to be treated, while the higher range of alloy content should be used with the lower carbon for large dimensions.

Having in mind the foregoing admonition a steel suitable for various requirements may beproduced within the following percentage limits:

As an illustrative example of a formula to be followedby the steel mill wishingfor a composition to aim at in melting steel for anti-friction bearing race rings, to have a maximum section 1 perof. approximately M, of an inch, we would give the following formula:

Carbon m-.. 1.00 Manganese 1.00 Silicon .6 Chromium the rest being substantially iron.

In regular practice in the steel mill the result, of. course, would be outside of this preferred analysis so that, for instance, manganese, silicon and chromium would vary from -10. to points from the average, and carbon :5 points.

If a steel is desired for sections up to 1% inches we would specify an alloy steel with the following mean analyses:

Silicon .7 Chromium 1.3

For still larger sections we would specify an alloy steel with the following mean analyses:

Silicon .8 Chromium 1.6

Carbon Chromium -.'90' 2I5o the rest being substantially iron, the sum of manganese, silicon and chromium being not less than 2 nor more than 5%, a lower range of alloy content being present with the higher carbon, and a higher range of alloy content being present with the lower carbon.

2. An alloy steel which will permit deep hard ening to satisfactory structure and good endurance when an article formed therefrom with a. maximum section of seven-eighths of an inch is quenched in oil from above the critical range, the analysis being approximately:

Percent Carbon 1.00 Manganese 1.00 Silicon .6 Chromium 1.00

the rest being substantially iron.

3. An alloy steel which will permit deep hardening to satisfactory structure and good endurance when an article formed therefrom with a maximum section of one and one-quarter inch is quenched in oil from above the critical range, the analysis being approximately:

, Percent Carbon .95 Manganese 1.50 Silicon .7 Chromium 1.3

the rest being substantially iron.

4. An alloy steel which will permit deep hardening to satisfactory structure'and good endurance when an article formed therefrom having a section larger than one end one-quarter inch is quenched in oil from above the critical range, the analysis being approximately:

Percent Carbon .9 Manganese 2.00 Silicon .8 Chromium 1.6

the rest being substantially iron.

5. A bearing part made from an alloy steel deep hardened by quenching in oil, and having ap proximately the following percentage range of analyses:

Carbon 1 .85 Manganese 80-300 Silicon 501.50 Chromium .90-2.50

the rest being substantially iron, the sum of manganese silicon and chromium being not less than 2 nor more than 5%; the lower range of alloy'content and the higher carbon being present in parts of smaller dimensions of material and the higher range of alloy content being present with the lower carbon in parts of larger dimensions.

JOEL LARSSON. HAAKON STYRI. 

